1. Field of the Invention
The present invention relates to an improved lens grinding lap cover. In another aspect, this invention relates with a method of preparing the novel lap cover.
2. Description of the Prior Art
The process of lens grinding and polishing has been carried out, according to recorded reports, for nearly four centuries. In the process, slabs of optical material, such as glass or optical grade plastic, are cut with a saw or slitting disc, formed into a desired shape by chipping or heating to a conformable consistency and pressing in a mold to produce a lens blank. The surfaces of the lens blank are then ground, or lapped, to the desired form on a cup-shaped iron tool or lap of the correct curvature, if the lens is convex, or on a dome-shaped tool or lap, if the lens concave. Early methods involved supplying abrasive slurry to the lap-lens interface for grinding and polishing which did not prevent the concomitant erosion of the lap surface from the required curvature. Recent developments included the use of an overlay or lap cover, shaped to conform to the curved surface of the lap, which protects the lap surface and prevents destruction of its curvature. Such lap covers may have an abrasive coating provided by a permanent coating of a mixture of a resin binder and abrasive particles or by supplying abrasive particles in a liquid vehicle (employing a foil or fabric-type lap cover) during the lapping operation.
Such lap covers are known in any of a wide variety of shapes. For example, Stoppacher (U.S. Pat. No. 3,959,935) discloses a cover shaped somewhat like a modified four leaf clover. Faas (U.S. Pat. No. 3,144,737) discloses a similar abrasive lap cover. Fenton (U.S. Pat. No. 2,282,650 and 2,309,836) discloses lap covers having a plurality of petals or leaves emanating from a central connecting portion. Hoenig (U.S. Pat. No. 3,324,608) discloses a generally circular shaped lap cover having four equally spaced radial slots. U.S. Pat. No. 3,699,721 discloses a slotted distorted cross-shaped lap cover.
Each of these lap covers suffers from a common deficiency. None can be cleanly stripped in one piece from the lap surface by merely detaching one portion of the lap cover in stripping off the entire lap cover. Most require detachment of two appendages or more before the entire lap cover can be removed from the surface to which it is attached and even then it often cannot be removed in one piece. This is both inconvenient and time-consuming.
Another common problem associated with the lap covers of the prior art is the considerable amount of waste material (or "weed" as it is called in the art) left after each lap cover is cut from a bulk sheet. None can be cut to minimize this waste. The lap cover configurations of the prior art not only produce considerable waste or weed but their complex shapes make them much more difficult to convert (i.e., cut and separate from the weed), increasing their production costs and time.